REPRODUCTION OF FUNGIREPRODUCTION OF FUNGIBy Assoc.Prof Dr.Mohd Noor Abd.Wahab

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Sub-topicSub-topicMold-Yeast DimorphismAsexual Reproduction of FungiSexual Reproduction of Fungi

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Mold-Yeast DimorphismMold-Yeast Dimorphism

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Fungi ReproductionFungi Reproduction Mold-Yeast Dimorphism Some fungi have the ability to alternate between a mold form and a that of a

yeast form -dimorphic fungi Dimorphism occurs in response to environmental factors, of which no one

common factor regulates the morphological switch in all dimorphic fungi.

e.g., Histoplasma capsulatum - mold at 25°C, yeast at 37°C e.g., Mucor rouxii - mold with the presence of oxygen, yeast in the absence

of oxygen

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Differences in cellular signaling and regulatory factors

Environmental signals often affect cellular behavior through a signal transduction pathway leading to altered metabolism or gene expression.

The intracellular factors involve in this include calcium and calcium-binding proteins, pH, and cyclic AMP.

intracellular signaling compounds are associated with phase transitions, as messengers and mediators.

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Mold form : growth in mold form occurs by production of multicellular filamentous colonies. These colonies consists of branching cylindric tubules

called hyphae.The mass of intertwined

hyphae that accumulates during active growth is a mycelium.

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Yeast form : Yeast are unicellular form of

fungi and they reproduce by budding

(eg:Crypotococcus and

candida)

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To identify the control of the dimorphic switch

To identify the basis of dimorphism -grow a fungus in condition that are nearly as identical

as possible except for one factor that changes the growth form.

Then the populations of M(mycelial) and Y(yeast) forms can be compared for their differences in biochemistry, physiology, and gene expression.

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Biochemical compositionThe cell wall component In Mucor rouxii the Y form has more mannose than the M form; In Paracoccidioides brasiliensis the Y form has α -1,3

glucan,whereas the M form has β-1,3 glucan; In Candida albicans the M form has more chitin than the Y

form; In Histoplasma capsulatum and Blastomyces dermatitidis the

M form has less chitin than the Y form.

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Differences in gene expressionDifferences in gene expression in the M and Y phases

can be detected by extracting messenger RNA and comparing the mRNA binding patterns by gel electrophoresis.

In several cases it has been shown that a few polypeptides are constantly associated with only the M or the Y phase.

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Fungus Conditions For mycelial growth

Condition for yeast -like growth

Human Pathogens

Histoplasma capsulatum 20-25 °C 37°C

Blastomyces dermatitidis 20-25 °C 37°C

Paracoccidioides brasiliensis 20-25 °C 37°C

Sporothrix schenckii 20-25 °C 37°C

Coccidioides immitis 20-25 °C 37°C

Candida albicans Low nutrient High nutrient

Saprotrophs

Mucor rouxii and some Zygomycota

Aeration Anaerobiosis

Plant pathogens

Ophiostoma ulmi High Calcium Low Calcium

Phialophora asteris Nitrogen Flooding with water

Ustilago maydis Dikaryon Monokaryon

Insect pathogen

Beauveria bassiana Solid media Liquid culture11

Blastomyces dermatitidis• Specimen: Sputum• Stain: Gram Stain• Magnification: x1000

Histoplasma duboisii• Specimen: Bone• Stain: GMS• Magnification: x1000• Structure: Large cell size, oval to spherical narrow attachment creating "double cell or figure eight" appearance.

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Histoplasma capsulatum• Stain: Lactophenol Analin Blue (LPAB)• Magnification: x400

Blastomyces dermatitidisi• Specimen: Broncho alveolar lavage (BAL)• Stain: Calcofluor White• Magnification: x400

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Asexual Reproduction of Asexual Reproduction of FungiFungi

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Asexual reproduction of Asexual reproduction of fungifungi

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Reproductive structuresReproductive structures

• reproduction in fungi occurs by spore formation.•bacterial endospores survive adverse environmental condition. It is also not reproduction bcoz it does not increases the total number of bacterial cells.

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fungal spore detach from parent and germinates into a new mold

------ true reproductive spore = one organism produce many spore.

» but it do not exhibit the extreme tolerance and longevity of bacterial endospores.

» by depending of species, it form from the aerial mycelium.

» can be asexual or asexual.

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Difference between sexual Difference between sexual and asexual sporeand asexual sporeSexual spore

☺result from fusion of nuclei from two opposite mating strain of same

species

☺have both genetic character of

parental strain

Asexual spore ☺form from aerial mycelium of one

organism

☺when spore germinate, It will be identical with

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Asexual sporeAsexual spore☺ produce by an individual fungus through

mitosis and subsequent cell division

☺ there is no fusion of the nuclei of cell

☺ 5 type : ~ arthrospore ~ chlamydospore ~ sporangiospore ~ conidiospore ~ blastospore

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SporangiosporesSporangiospores¤ is an asexual spore formed

within a sac at the tip of an aerial hypha called sporangiophore.

¤ each sporangium can contain hundreds of sporangiospores

¤ eg ; rhizopus

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Conidiospore

¤ is unicellular or multicellular spore that is not enclosed in sac

¤ conidiospore produced in a chain at the end of conidiophore

¤ eg ; Penicillium

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Arthrospores Arthrospores ¤ is formed by the fragmentation of a

septate hypha into single , lightly thickened cells

Eg: coccidioides immitis

Blastospores¤ consist of a bud coming off the parent

cell Eg : some yeast

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ChlamydosporesChlamydospores

¤ a thick-walled spore formed by rounding and enlargement within a hyphal segment

Eg : Candida albicans

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Sexual Reproduction Of Sexual Reproduction Of FungiFungi1. Chytridomycetes2. Zygomycetes3. Ascomycetes4. Basidiomycetes

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Sexual Reproduction of Sexual Reproduction of FungiFungiSexual reproduction introduces the

possibility of variation into a population.It is necessary to have two mating type

haploid nuclei (n + n), or a diploid (2n) nucleus.

A diploid first, but once fused the nuclei undergo meiosis, which is the reduction division that potentially brings about variation in the progeny.

Then, followed by the formation of spores.

In most case, spores are resting spores that can withstand adverse conditions.

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A fungal sexual spore results from sexual reprodution, which consist three phase:

i.Plasmogamy : A haploid nucleus of a donor cell (+) penetrate the cytoplasm of a recipient cell (-).

ii.Karyogamy : The (+) and (-) nuclei fuse to form a diploid zygote nucleus

iii.Meoisis : The diploid nucleus gives rise to haploid nuclei (sexual spores), some of which may be genetic recombinant.

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Sexual SporesSexual SporesChytridiomycota

Zygospores

Ascospores

Basidiospores

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Sexual Reproduction of Sexual Reproduction of ChytridiomycetesChytridiomycetes

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Production of diploid spores after gametic or somatic fusion of two different mating types.

The resulting spore may germinate to produce a diploid vegetative mycelium.

It may undergo meiosis to produce a haploid mycelium.

The diploid mycelium can also produces resting sporangia in which meiosis occurs, generating haploid zoospores that germinate to produce haploid vegetative mycelium.

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Sexual Reproduction of Sexual Reproduction of ZygomycetesZygomycetes

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Occurs if food ecomes scarce or environmental condition become unfavorable.

Requires compatible strains :(+) mating strain(-) mating strain

When the two mating strains are closed, pheromones hormones produced.Cause their hyphae to

form projections called progametangia that mature to gametangia

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After fusion of gametangia, fuse to form

The zygote develops a thick, rough, black coat and become a dormant zygospore.

Meiosis often occurs at the time of germination.

the nuclei of the two gametes

a zygote

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The zygospore then splits open and produces a hypha that bears an asexual sporangium to begin the cycle again.

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Sexual Reproduction Of Sexual Reproduction Of AscomycetesAscomycetes

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Sexual reproduction in Sexual reproduction in AscomycetesAscomycetes

- Sexual spores are produced in small sac-like structure called ascus. - Sexual spores are produced on ascus called ascospores.

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In sexual reproduction, haploid mycelia of opposite mating strains fuse.

In this group of fungi there are no specialized organs of hyphal fusion, different mating type mycelia merely fuse with each other to form dikaryons, mycelia with two mating type nuclei within it.

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The dikaryotic mycelium can differentiate to from varying amounts of sterile mycelium around what is to become the fertile tissue of the fruit body.

In yeasts, a single, diploid yeast will undergo meiosis, producing four haploid progeny cells, but in more complex fungi there are a sequence of cellular and nucleic events that ensure an organized fertile layer.

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Sexual Reproduction of Sexual Reproduction of AscomycetesAscomycetes

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Neurospora crassa

Sexual Reproduction of Sexual Reproduction of BasidiomycetesBasidiomycetes

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BasidiomycetesBasidiomycetesMost complex and larger

structureRarely produce asexual sporeSexual spores externally from

basidium4 basidiospores in each basidiumMuch of their life cycle spent as

vegetative mycelium, exploiting complex substrate

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Life Cycle of Life Cycle of BasidiomycetesBasidiomycetesHaploid basidiospores germinate,

grow into short-lived myceliaUndifferentiated hyphae from 2

haploid mycelia of opposite mating type undergo plasmogamy

Form dikaryotic myceliumGrows up into a fungi capable of

creating its own mushrooms(fruiting structure).

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The mycelium of the mushroom forms mycorrhizae with trees.

Environmental factors such as rain, temperature changes, and, for mycorrhizal species, seasonal changes in the plant host, induce the dikaryotic mycelium to form compact masses that develop into mushrooms (fruiting structure).

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Karyogamy occurs in the terminal dikaryotic cells that line the surfaces of the gills.

Each cell swells to form a diploid basidium, which rapidly undergoes meiosis and yields four haploid nuclei.

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The basidium then grows four appendages, and one haploid nucleus enters each appendage and develops into a basidiospore.

Mature basidiospores are often discharged explosively when raindrop or an animal touches the mushroom.

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ConclusionConclusionYeast-mold dimorphism i. Environmental factor ii. Intercellular factorAsexual Reproduction i. Budding ii. Fission iii. Hyphae fragmentation iv. Spore formation (5 types)

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Sexual Reproduction i. Plasmogamy ii. Karyogamy iii. Meiosis

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